Epoxy coating systems cured with polyamine-based curing agents are used for the preparation of industrial maintenance coatings and other types of protective coatings for a variety of substrates. Epoxy resins have excellent resistance to chemicals also have good adhesion to most substrates, e.g. various woods, wall-boards, metals and masonry surface.
There has long been a desire to formulate a curing agent which is essentially free of volatile organic compounds (VOC's), which are self emulsifiable and curable at a wide range of temperatures in the absence of external accelerators if possible.
Many of the current waterborne epoxy resins and curing agents are plagued with the problem of poor film properties because the surfactants tend to migrate to the surface during the cure of the resin system. Thus, it would be desirable to provide a curing agent system containing a surfactant which does not migrate during cure, that is, a water compatible system which does not require salting the surfactant, e.g. with acids, or using plasticizers to form a stable dispersion of the curing agent in water.
Water compatible curing agents can be soluble (homogenized), dispersible (oil-in-water dispersions), or provide water-in-oil dispersions.
In addition to providing a water compatible curing agent, the curing agent should be readily compatible with a waterborne epoxy resin in order to make a coating having good mechanical and resistance properties. A waterborne curing agent that does not have good compatibility with the epoxy resin will coalesce poorly when applied onto a substrate. The problem of compatibility is more acute where the curing agent primary amine groups have been converted to secondary amine groups to reduce the blooming or hazing phenomena due to carbamation.
It is desirable to obtain curing agents that are water compatible and provide cured products with good mechanical and resistance properties.